I tried this with my Surface Pro (there were only 128GB availible
) .. SD-Cards are VERY slow, even compared to harddrives. I got a 64GB SanDisk (I think it's a SanDisk, I'm not sure at the moment). It's ok to store your pictures, music and such things, but I don't recommend to install any programs. I have some old games installed on it but if you try to use any newer software it will be extremly slow. I once had VisualStudio installed on the SD and it took about an hour until an update was installed (on normal HDD about 3 Minutes).